Enrichment Of Polycyclic Aromatic Hydrocarbons Anaerobic Digestion By NO₃^-/SO₄^2- Electron Acceptor And Study Of Microbial Community Response

Polycyclic aromatic hydrocarbons(PAHs),as the main persistent organic pollutants in oil,have attracted much attention due to the increasingly serious pollution caused by oil leakage and discharge in the process of oil exploitation,transportation,loading and unloading,processing and use.Due to the complex structure,strong hydrophobicity,and difficulty in biodegradation of PAHs,penetrating deep into soil or groundwater layers can cause persistent pollution.To solve these problems,this research takes PAHs pollution in the anaerobic digestion(AD)system as the research object,selects naphthalene(Nap)as the representative pollutant of PAHs,carries out the research on the long-term pollution response of AD system to PAHs and the mechanism of nitrate and sulfate electron acceptor enhancing anaerobic microbial degradation of PAHs,and clarifies the impact of electron acceptor on the electron transport system of anaerobic digestion microbial community.This provides a scientific basis for improving the efficiency of anaerobic microbial degradation of PAHs,and has important reference value and application significance.The main research findings are as follows:1.Long term research on AD of Nap shows that under methanogenesis,the removal effect of Nap was limited,and the maximum removal amount is only 5.38±0.54 mg/(L·d).Nap destroys the protein skeleton structure and causes the protein to become loose by attacking the C=C and C=O of proteins in extracellular polymeric substances(EPS).Molecular Operating Environment,MOE molecular docking simulation results showed that Nap changed the structure of key enzymes through the formation of hydrogen bonds,thereby affecting the progress of enzyme catalysis.The increase in EPS secretion by microorganisms,the activity of the electron transfer system(ETS),and the further increase in ATPase activity indicate that microorganisms resist the toxic inhibition of Nap by enhancing metabolic activity.In situ metabolism experiments and changes in microbial community abundance showed that longterm exposure to Nap significantly inhibited the activity of syntrophic bacteria,electroactive bacteria(Clostridium_sensu_stricto、Geobacter),and methanogens(Methanosaeta).Meanwhile,the abundance of functional genes such as mdh,IDH1,and complex Ⅰ related tothe electron transfer system.significantly decreased.2.Synergistic mechanism of different electron acceptor on anaerobic biodegradation of Nap.(1)When nitrate was added as the electron acceptor,93%of the electron flow(MEF)flowed to methanogens,7%of MEF flowed to denitrification bacteria,and the biological removal amount of Nap reached a maximum of 14.04±2.27 mg/(L·d).The addition of electron acceptor nitrate significantly enriched the electroactive bacteria Raoutella(0.4%to 38.4%).The abundance of functional genes IDH1,mdh,and complex I related to electron generation and electron transfer significantly increased.We have found for the first time that MAG.SDU 14 had the function of simultaneous denitrification and anaerobic biodegradation of Nap under the nitrate electron acceptor system.Meanwhile,MAG.SDU 14 could conduct electron and acetic acid interspecific feeding with MAG.SDU 37 to maintain methanogenesis and achieve efficient anaerobic biodegradation of Nap.(2)When sulfate was added as the electron acceptor,69.2%of MEF flowed to methanogens and 30.8%flowed to sulfate reducing bacteria(SRB),the highest value of Nap biodegradation was 26.08±4.47 mg/(L·d).The Nap biodegradation bacterium Desulfovibrio was significantly enriched.Nap inhibited the encoding of enzyme IDH1 and sdhABCD genes involved in electron generation,as well as the encoding of enzyme complex Ⅰ and Ⅱ genes involved in electron transport,while sulfate alleviated this inhibition.The key gene ubiD for anaerobic biodegradation of Nap significantly increased by 1.80 times with the addition of sulfate.In the sulfate electron acceptor system,the metagenomic analyses showed that the anaerobic biodegradation of Nap depended on interspecific feeding and electron transfer between MAG.SDU 1,MAG.SDU 45 and MAG.SDU 37,which ensured the efficient anaerobic biodegradation of Nap.